Encryption devices are known that both increase the speed of encryption processing and also improve the cryptographic strength (Japanese Patent Application Laid-Open (JP-A) No. 2003-241656). In such encryption devices, plain text D is divided and output as plural divided data sets by an initial processing function, the plural divided data sets are then expansion-substituted to the same size as an encryption key K by a calculation function, with the calculation function modifiable through a coefficient. The coefficient is generated by a parameter generation section. A non-linear encryption block processing section then non-linearly encrypts the divided data and the encryption key K as a variable, and outputs encrypted plural divided encrypted data. Then in a post processing function, an inverse function to the calculation function is employed to compression-substitute the divided encrypted data to the same size as the divided data, the divided data is then combined and output as encrypted text, with the inverse function calculation function modifiable through a coefficient.
An encryption processing device is also known including: means to mask secret data a, b, and compute masked secret data A, B by computation of an exclusive logical sum between the secret data a, b and random number data m1, m2; means to compute intermediate values Temp1 to Temp3 to remove the mask from the masked secret data A, B using the masked secret data A, B and the random number data m1, m2; and means to calculate the logical product or the logical sum of the secret data a, b using the masked secret data A, B and the intermediate values Temp1 to Temp3 (JP-A No. 2009-005164).
The encryption processing technology described in JP-A Nos. 2003-241656 and 2009-005164 strive to achieve high speed encryption processing and higher security; however, they have issues such as potential danger due to the possibility of being solved logically. In order to alleviate such issues, sometimes the volume is increased, at the expense of speed, and they are not technology that as a whole satisfies the demands of encryption processing for “speed”, “security”, and “lightness”. To address this, an encryption method has been proposed based on an irreversible function that is not logically solvable (L. Accardi, M. Regoli, M. Ohya, “The QP-DYN Algorithm”, QP-PQ 28, Quantum Bio-Informatics IV, 1-16, 2011).